At the October meeting, Paolo Marcassoli from Cescor gave a very interesting talk on the use of Finite Element Method (FEM) in Cathodic Protection Design. Paolo introduced the advantages of FEM modelling, explained its mathematical principles and presented case studies where the technique had been implemented.
Over the past few years the use of computer aided approaches have improved the design of galvanic and impressed current cathodic protection systems. To ensure that protection conditions are achieved at each point of the structure, correct anode spacing is critical. FEM allows accurate analysis of structures with complex geometries, and the impact of various factors on corrosion control, providing precise prediction of protection current distribution.
FEM is a numerical technique for solving boundary value problems, it minimalizes an error function, generating a stable solution. It solves simple equations over small subdomains, i.e. finite elements, to approximate more complex equations over a larger domain. Such analysis considers both, the primary current distribution related to electrolyte resistivity and the secondary current distribution related to electrode reactions. Boundary conditions are characterized by electrochemical behaviour of the metallic surface under protection, for example through the Tafel equations. The electrical field is then solved using Laplace equation.
The first case study demonstrated the application of FEM on an above ground crude oil storage tank, where the bottom of the tank was protected internally by coating and galvanic anodes, flush-mounted type or zinc ribbon, depending on the water hold-up. This case is described in more detail in the article on page 14. In the second case study Paolo presented how FEM benefits retrofit CP design of offshore assets. This included applications in: offshore platform protected by galvanic anodes, offshore platform retrofitted by impressed current system, subsea pipeline retrofitted by galvanic anode sleds, and Single Point Mooring retrofitted by galvanic anodes clamp and pods. The study showed that FEM modelling in cathodic protection design is a very useful tool that helps to ensure thorough protection of the asset and possible reduction of costs by optimization of anodic system installation, and determining need for a new retrofit system.
This was an excellent talk and was well received by the audience. The technique presented is currently widely used in the industry and is recognized by professional organisations. It surely is a step forward in cathodic protection design and will continue to develop in the future.
The November meeting was devoted to the presentations from the Young Engineers on the results of their YEP case study of a heat exchanger failure. This was the culmination of 12 months of study by the delegates who have worked through modules that span the breadth and depth of the technologies used in our industry.
It was a truly fantastic evening with 3 excellent presentations from the teams
Stephen Shapcott Liya Guo
There was a good deal of questions from the audience after each presentation and following which the judges retired to deliberate. Bill Hedges from BP, on presenting the award, said how hard it had been to select a winner as they were all so good. However there has to be a winning team and that was Team Doggett, who will be travelling to the USA in April 2019 to attend the NACE Conference in Nashville, where a whole programme of events will be arranged. They will post a blog of their activity and learnings on a daily basis on the Institute website. The organisers are grateful to the President and staff of NACE for pledging their support to the winners whilst they are in Nashville by providing free conference registrations, and access to the student award ceremony.
The winning team will also present their conference learnings during the London branch 2019 winter series lectures.
The response from the delegates attending this programme has been incredibly encouraging;
“This programme has altered the way I think about my work and how I carry it out”
“I have found a new job and moved to London living in Kew Gardens and cycling to work each day. I love it”
“I hadn’t realised the value of ICorr and I will go back to work on Monday and encourage them to engage”
A comment from one of the senior engineers in our fraternity gave the programme even more credibility, “This is probably the most important function in the UK Corrosion calendar, it’s truly fantastic”
It’s also interesting to note that Agnieszka of Team Boran, travelled from Poland in 2015, under her own steam, to hear the previous YEP case study presentations, and decided then she wanted to be involved in the next YEP programme.
Thanks go to all those involved in the process; the organising committee, the lecturers, the hosts, the mentors, the judges, the delegates, and if course a big thank you to the sponsors of the event, BP.
The second joint meeting of the branch with the SCI London Group was held on 25 October, at their prestigious headquarters in Belgrave Square. This ultra-modern auditorium made for a most comfortable setting and was enjoyed by an attendance of over 60.
The evening chairman, John T O’Shea, a Past President of ICorr, began the procedures by thanking Dr Fred Parrett, currently Hon. Treasurer of the SCI London Section, for all his work in helping to organise this event.
The first presentation “A Fighting Ship” was based around the Mary-Rose project at Portsmouth. This was given by Professor Eleanor Schofield, Head of Conservation and Collections Care at the Mary Rose Trust. Eleanor graduated from Imperial College, where she also received her PhD in Material Science. She has recently received an Honorary Chair at the University of Kent, at Canterbury.
Professor Schofield began her talk by correcting the too often quoted story that the Mary Rose sank in 1545 on her maiden voyage. In fact she was built in 1510 and served for 34 years as the flagship of Henry VIII’s navy in many battles, particularly in wars against France. Following the lifting of the ship out of the seabed mud, the timber hull was treated over many years by spraying with water and polyethylene glycol to prevent further deterioration once it was exposed to the air.
Perhaps less well known is the work in restoring and maintaining over 19,000 artefacts that had also been recovered. A significant part of the collection was the 1200 + iron cannonballs, which had been exposed to sea-water since the ship sank, and which were in danger of corrosion when exposed to the air due to the chloride in sea-water. It was vital that ways were found of preserving the these, as it was recognised that while the cannons were made to last and be used many times, the cannonballs were only needed for a one-off use, and thus greatly inferior in their quality and standard of manufacture.
Initially researchers attempted to remove chloride from the cannonballs, by soaking in water with and without chemical treatment. Chloride reduction by heating in an atmosphere of hydrogen was also attempted, but unfortunately these methods did not successfully prevent disintegration when they were later put on display. To better understand this problem, Professor Schofield, established a joint research project with the department of archaeology at UCL and the UK Diamond Light Source in Didcot which is the UK’s national synchrotron. This works like a giant microscope, harnessing the power of electrons to produce penetrating bright light X-rays, which combined with absorption spectroscopy, and fluorescence mapping, made it possible to visualise the differences in the corrosion profiles. These could be traced to the treatments applied in the 35 years since the cannon balls were recovered with the Mary Rose. The results revealed detailed maps of the elements involved in the corrosive process, giving an unprecedented insight into conservation on a molecular scale. This crucial information will help to protect these and other cultural heritage artefacts for many decades to come.
The second presentation, “Fighting Corrosion” was given by Jim Glynn, a previous chairman of London Branch. Jim concentrated on the “dynamic duo” of corrosion protection – a suitable protective coating as the primary source of defence, supported where appropriate by a cathodic protection system to prevent any corrosion occurring at areas of coating damage.
It is often commonly believed that rusting is a simple, chemical oxidation reaction – but it is not. Aqueous corrosion is a complex, multi-stage step process which includes electron transfer at the molecular level. Thus these electro-chemical reactions during corrosion can be influenced by the external application of electrical potentials. Under the right circumstances, corrosion can be stopped by applying the appropriate level of negative potential using a DC current supply.
Jim presented many examples where the correct conditions of a good coating and a suitable working cathodic potential were present. However, he also described many examples where this was unsuccessful. These included a pipeline coating that had totally disbonded and broken away from the pipeline, due to a higher potential than required being applied, which generated hydrogen gas on the surface of the pipeline, causing the coating damage.
He also described Thermally Sprayed Aluminium (TSA) applications, which are excellent protective coatings when properly applied. The aluminium content can act as its own in-built cathodic protection anode. However, in the wrong environment, the aluminium can be quickly used up, and premature failure occurs.
Jim expanded his presentation to compare recent case studies of retro-fitting remote anode beds to two similar North Sea platforms which had exceeded their design life, but it was decided that the protection of these structures subsea could be extended using additional cathodic protection. One had been fully coated with coal tar epoxy, while the legs on the other had been left bare, but with a built-in corrosion factor that should have exceeded its expected life. The coated structure required a current output of 1,000 Amps, while the bare steel legs needed around 7,500 Amps, to produce the correct negative potentials, with these high DC currents supplied by banks of adjustable transformer rectifiers located on the platform decks.
Jim also interspersed a number of quiz questions, asking the audience to identify some notable “Dynamic Duos” in life, film and comic books, which was well received and considered a fun way to conclude the presentations.
The vote of thanks was given by Dr Parrett and he presented the speakers with ICorr engraved pens, as a memento of the evening, which was followed by refreshments and networking in the Garden Rooms.